The process of compression molding has grown to be ever so common. The product used in and produced by the process of compression molding is termed sheet molding compound or SMC. Compression molding was developed for replacement of metal components with composite parts. The molding process is typically carried out with either thermosets. Typically, a thermoset charge is placed in a two-piece heated mold which is subsequently closed and held at a high pressure. This initiates a thermal setting cure reaction. Typical products manufactured by compression molding include front and rear end vehicle panels, hoods, roofs, fenders, spoilers, and air deflectors.
Many SMC products are filled with fibers, such as glass fibers. Glass fibers provide strength and stiffness. U.S. Pat. No. 5,484,652 to Strunk et al. involves a material for smoothing the outside surface of a woven fabric composite lay up in which a layered sandwich structure is formed of continuous fiber woven material, resin films and a mat of randomly oriented discontinuous fibers. The sandwiched layers are integrated into a single sheet of resin impregnated material by application of pressure and heat.
However, costs for painting or coating glass fiber-filled SMC products can be reduced. Typically, a conductive primer is applied onto glass fiber-filled SMC products before color painting or coating the product. The conductive primer provides for the ability to electrostatically paint or coat the SMC product. Because glass fiber-filled SMC products are not conductive, without application of conductive primer onto the SMC product, subsequent painting or coating onto the product would result in a low efficiency paint transfer upon the product surface. This results in higher costs and increased time of production. If the manufacturing step of applying conductive primer onto the SMC product can be eliminated, then substantial cost savings would be experienced.
Moreover, as the price of glass fibers remains stagnantly high and the price of automotive carbon fibers continues to decrease, feasibility and demand to use automotive carbon fibers in lieu of glass fibers in SMC products grow. Generally, carbon fibers are more expensive than glass fibers, but add greater strength and stiffness when used in SMC products. Carbon fibers are also lighter weight than glass fibers at comparable fiber loading.
What is needed is an automotive carbon fiber-filled SMC product that provides for electrostatically painting or coating the product without applying a conductive primer.
What is also needed is a method of making a carbon fiber-filled SMC that has high stiffness and strength.